Soft tissue sarcomas are solid tumors derived from mesenchymal cells of muscle, connective tissue, and cartilage. Malignant fibrous histiocytoma (MFH), the most aggressive and most commonly diagnosed subtype of sarcoma is highly metastatic. Intratumoral hypoxia has been proposed to facilitate metastasis of sarcomas, including MFH, to distant sites. However, the molecular basis of this process is unknown. Recently, hypoxia inducible factor (HIF)11 and several of its transcriptional targets, including the transcription factor FOXM1, have been identified as markers of metastatic MFH sarcoma by microarray analysis. Regulation of FOXM1 expression may be particularly important in sarcomas, as FOXM1 has been associated with tumor formation and metastasis in numerous other human cancers. Both HIF and FOXM1 are potential downstream effectors of the Ras pathway and Ras mutations are found in up to 50% of MFH tumors. The central hypothesis of this proposal is that HIF activity is increased in hypoxic sarcomas, promoting expression of FOXM1 and metastasis. Based on this hypothesis I will pursue three specific aims. Specific Aim 1: To determine the effects and underlying molecular mechanisms of hypoxia and HIF on proliferation, apoptosis, and senescence of sarcoma cell lines in vitro. Specific Aim 2: To define the effects and molecular basis of hypoxia and HIF- mediated migration/invasion and oxidative stress responses in sarcoma cell lines. Specific Aim 3: To examine the role of HIFs and FOXM1 in vivo using an inducible mouse model of sarcoma and human xenograft tumors. To complete these studies I will combine in vitro and in vivo methods of cell biology, biochemistry, immunohistochemistry, genetics, and animal modeling. The objective of this research proposal is to elucidate the underlying mechanisms of hypoxia and HIF-dependent sarcoma formation and progression. The long-term goal of these studies will be to identify novel therapeutic targets, which will facilitate new treatments for sarcoma and provide important clues about general tumor formation and metastasis to the lung.